Varnished Paintings Solve Uneven Surface Shine

October 31, 2009

One of the reasons to varnish a painting is that it can unify the surface quality. In this image of a recent painting of mine shown below, when you look straight at the painting it appears fine, but at this angle of reflected light the surface shine is uneven from matte to glossy. This matte effect is sometimes described as “sunken in” and a number of factors can create it.

The chief issue is related to absorption. Any paint media can have this problem, whether it’s oils, acrylic, gouache, or casein. The main constant with all of them is the pigment in the paint, but that’s not the only cause. The surface itself might be absorbent, like raw paper or gesso, or if you’re painting in layers then that paint surface may have varying degrees of absorbency. Some paints may also contain additives like surfactants, driers, or wax that can alter their shine. Some oil mediums, like stand oil, are glossier than others.

There are a number of ways to deal with this patchy shine. The best solution with some media is to varnish the painting. Unfortunately, I don’t recommend varnishing watercolor or gouache, since it can alter or damage the painting and can’t be removed, and some exhibitions require anything on paper to be framed behind glass anyway. Since it only shows up opposite reflected light, one option is to just hang the unvarnished painting in a location where you can’t see any reflection. That’s not always possible, however, and sometimes you have no control over where it’ll hang in a show or someone’s home.

Even though this effect happens with acrylics also, it’s a simple solution to just rub acrylic medium over the dried paint to even out the shine. You shouldn’t really do that with oils since it isn’t intended to be used like a varnish. Varnishes should be removable, but mediums aren’t, and can cause yellowing problems as they age.

Another option is to manage what paints you use and when. This may mean your initial layers can have more absorbent pigments, and the top layers use less or none of those. That’s quite a bit of trouble to go through just to avoid a shiny surface, and forces you to restrict your choice of pigments. Personally, I’d rather not concern myself with that and resolve the issue when I’m finished. Nonetheless, it’s a good idea to be familiar with your paint’s surface quality. In the images below you can see an example of various commercial gouache paints. I painted them on glass so they wouldn’t be effected by the surface absorbency. I recommend doing this test with all your paints in whatever medium you use.

Paint swatches

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In the case of my casein painting, it will be possible to safely varnish it. Right now it will be too fragile for any wet treatment, so I need to wait several months for it to cure. What I then do is add an isolation coat of permanent acrylic medium, and then add a coat or two of removable spirit varnish on top of that. That is how acrylics are varnished. If the work has to leave my hands before then, I’m forced to treat it as I would a watercolor and frame it under glass, or ask the buyer to return it later for varnishing.

The best solution for an oil painting is to varnish it also. A temporary varnish (retouch) can be applied after the final layer has dried which may take a couple weeks, depending on how it was painted. A retouch may not completely restore an even shine, but will do in the short term. Once the oils have completely cured then a final varnish can be applied.